The invention arose during continuing development efforts toward improved marine drive water pumps, and particularly a pump impeller for a rotary vane positive displacement pump.
A rotary vane positive displacement pump has a pump driveshaft extending axially through a pump housing having a circumferential sidewall defining a pumping chamber. An impeller has a hub portion driven by the driveshaft and a plurality of flexible vanes extending radially outwardly therefrom in the chamber and having outer tips engaging the sidewall. During rotation of the driveshaft, the vanes move through portions of varying flexure to draw water or other pumped media in through an inlet and discharge same through an outlet. The vanes must be pliable enough to flex and enable rotation and pumping action, yet stiff enough to engage or remain adjacent the sidewall, in order to maintain water pumping efficiency and sufficient pump pressure capability. If the vanes are too flexible, the outer tips of the vanes do not remain close enough to the sidewall, and too much water flows past the vanes between the outer tips and the sidewall, which in turn reduces water pumping efficiency and pump pressure capability. There is thus a trade-off between flexibility and stiffness of the vanes, which presents a problem in the prior art.
Another problem in the prior art, in a marine drive, is poor air pumping efficiency, which in turn limits the height to which water can be drawn to the pump, or at least presents priming problems. In a marine drive, the lower the water pump, the less air has to be pumped before water is drawn upwardly to the pump. Conversely, the higher the pump the more air has to be drawn and pumped. Poor air pumping effiency means that a marine drive water pump may need to be mounted at a lower location on the gearcase than otherwise desired.
The present invention addresses and solves both of the above-noted problems. The invention provides impeller vanes which are flexible enough to enable pumping action, yet which act as very stiff members providing a high pressure head and increasing pump pressure capability, solving the above noted trade-off problem. The invention also improves air pumping efficiency, providing improved priming, and enabling considerable design flexibility in the vertical placement of a marine drive water pump, i.e. the improved air pumping efficiency provides a higher dry lift capability, which in turn enables the pump to lift water to a higher level to reach the pump.
By solving both of the noted problems, individually and in combination, the invention has widespread application, particularly where higher pressure and/or higher dry lift is desired.